Good old nagios! Nagios is a great Open Source Monitoring Server that monitors your servers and services/applications that is hosted on top of them, and has the ability to notify in the event when they go down.

I've been using Nagios for the last 7 years and worked for 3 business that chose Nagios as their preferred server monitoring solution.

All Nagios related posts are grouped under the #nagios category.

What we are doing today

Today we will setup a Nagios server and its plugins. The plugins helps to check different endpoints, such as custom tcp checks, ssh, snmp etc.

In this nagios tutorial series, I will publish a couple of post which will include:

  • Setup the Nagios Server and its Plugins - this post
  • Setup the NRPE Server and NRPE Client Server (this is nice for local ports or custom checks)
  • Setup Nagiosgraph (Graph performance data and add it as extra host configuration)
  • Setup a custom Bash and Python Nagios Plugin for Custom Checks
  • Setup a Telegram / Slack Plugin

Installing Dependencies:

Go ahead and install all the dependencies needed by nagios and add the nagios user and group:

$ apt update
$ apt install build-essential libgd-dev openssl libssl-dev unzip apache2 -y
$ apt install autoconf gcc libc6 make wget unzip apache2 php libapache2-mod-php7.2 libgd-dev
$ apt install libmcrypt-dev libssl-dev bc gawk dc build-essential libnet-snmp-perl gettext
$ apt install libcarp-clan-perl rrdtool php-rrd libssl1.0-dev
$ useradd nagios
$ groupadd nagcmd
$ usermod -a -G nagcmd nagios

Install Nagios

Download the nagios tarball from their website, have a look at for the latest version.

$ wget -O nagios.tar.gz ''

Extract the archive:

$ tar xpf nagios*.tar.gz
$ cd nagios-4.4.3/

Configure with nagios user and nagcmd group, install and change the ownership of the generated data:

$ ./configure --with-nagios-group=nagios --with-command-group=nagcmd
$ make -j4 all
$ make install
$ make install-commandmode
$ make install-init
$ make install-config
$ /usr/bin/install -c -m 644 sample-config/httpd.conf /etc/apache2/sites-available/nagios.conf
$ usermod -a -G nagcmd www-data

Install Nagios Plugins

Get the nagios plugins tarball, extract and install:

$ wget nagios-plugins.tar.gz ''
$ tar xpf nagios-plugins*.tar.gz
$ cd nagios-plugins-2.2.1
$ ./configure --with-nagios-user=nagios --with-nagios-group=nagcmd --with-openssl
$ make -j4
$ make install

Access Nagios

Enable apache modules:

$ a2enmod rewrite
$ a2enmod cgi

Setup basic auth for logging onto nagios:

$ htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

Setup a symlink for apache's nagios configuration

The configuration for the above will look more or less like the following:

$ cat /etc/apache2/sites-enabled/nagios.conf

         Require all granted
         AuthName "Nagios Access"
         AuthType Basic
         AuthUserFile /usr/local/nagios/etc/htpasswd.users
         Require valid-user

Create the systemd unit file for nagios /etc/systemd/system/nagios.service



ExecStart=/usr/local/nagios/bin/nagios /usr/local/nagios/etc/nagios.cfg

Reload the daemon:

$ systemctl daemon-reload

Enable the service:

$ systemctl enable /etc/systemd/system/nagios.service

Ensure nagios is started:

$ systemctl restart nagios
$ systemctl restart apache2

Access nagios on http://nagios-ip/nagios with the credentials that you configured earlier.

Up Next

In the next posts I will cover the following:

  1. Setup NagiosGraph for monitoring performance data
  2. Show you how to create a custom nagios plugin in python
  3. Create a Custom Notification service to send notifications to Telegram (or any API)

Thanks to Chris Liverani for the sweet cover photo!